Runs sh!t on optimax

[Uruk Hai]

I cant believe it, after reading loads of threads on here and numerous articles in magazines I decided for the first time since having my car to fill it up from empty with optimax. To my extreme dismay it doesn't run better or smoother it runs worse and lumpier and has a slight miss fire every once in a while, anyone know what this could be as its p!ssing me off to the back teeth 

[takethefifth]

Is it an 8v (digi or kjet) or a 16v?  I know my digi loves the stuff, something to do with the ecu automatically advancing the timing for it.

And did you run it to emptier than usual? (ie. could some crud from the bottom of the tank have got into fuel filter blocking it partially or something)

[AudiA8Quattro]

Could just be a dodgey load of fuel, or maybe you have drawn up some sh!t from the bottom of the tank. Its not recommended to run the tank too low.

[monzablue16v]

If it's a mk2 16v it won't adjust the timing to suit the RON of the fuel but if it misfires and runs rough it needs a tune anyway, choice of fill it with optimax forever and get it tuned on that or run it until the optimax runs out fill it back up with 95 ron. I found the same thing with my valver it pinked like a b!tch.

[Uruk Hai]

Sorry I should have put more detail its a 91  J plate 8V digi and I did run it quite low as I was seeing what I could get out of a full tank  . But last time I filled it up it was lower than when I put the optimax in and the fuel filter has only been on there for 2 months so surely it would have caught any crap going through the system. Is it possible its just taking a while for the E.C.U to adjust to the different octane as I haven't done 100 miles on it yet ? I just cant believe after all I've read about the experience of others that its made no improvement in mine, its not fair   

[takethefifth]

  I agree unlikely to be the filter at 2 months, my digi loves it just as soon as it gets down the fuel lines so i don't know whats up!

I've heard people talk about getting dodgy petrol but i've never experienced it myself in 11 years of driving so i am convinced it's an old wives tale! 

Couldn't be something else that has randomly gone wrong at the same time could it? Plugs, leads blah blah etc.. 

[rubjonny]

Sounds like you need to get it serviced, and I'd replace the blue temp sender.  Clean out the throttle body till its shiny as well

It may be your knock sensor isn't working right, or your timing is out.  Check out my digifant tuning guide in the maintenance+info section.

I must say that I haven't noticed a great deal of difference whenever I've filled up with optimax over Sainsburies 97 or Esso Premium, but it certanly didn't make it run rough!  Haven't tried it since the 2.0 conversion though so I guess I should give it a shot!

[...joe]

it'll probably take a couple of fills before you start to notice anything. they are old cars and you will have alot of crap caked on which, over time, optimax breaks down. i'd try it a few more times and take it on a nice long blast to see how it runs.

worth noting that as it does de-coke you're engine you might well be getting leaks round your valves (for example) as it starts to break it down. but to be honest i doubt that'd happen after 100 miles.

[Uruk Hai]

Thanks for all the advice, just to expand on the state of play the car has done 131K I never and I mean never rev it above 5K and I don't open the second butterfly when accelerating or go over about 75 mph. In the last 2 - 4 months I've changed the oil and filter, gearbox oil, fuel filter, air filter, coolant, cam belt and tensioner, cleaned out the throttle body and generally gone over the car to see if there was anything that needed doing. I'm no expert but it seems fine and didn't miss a beat until the morning after filling up with Optimax, I've had the car for 6 months now and this is the first time its run anything other than sweet. I might change the blue temp sender as I'm well aware of the difference this can make to the way the car runs, Joe maybe you have a point and it will run better as time goes by. If it doesn't its back to normal unleaded to see if that makes any difference. 

[VeeDubGTI16v]

it doesnt hurt to give it a good ragging now and again!